Hentai = pervert
Sukebe = lewd person
Ecchi = indecent
-kun = male-only suffix often used among children who are close friends
Ping's expression in the seventh panel is akanbe, a gesture of contempt roughly equivalent to a raspberry.
skillz = skills
Is Seraphim being a little too disapproving of Piro?

Piro speaks:
He's a self-persecutor, he beats himself up, he will always find what is wrong with himself and tear himself down at every opportunity, that's how he copes. It's not what his conscience (seraphim) says to him that is bad, its what he does with that information. Remember, she's an extension of HIS sense of morals, which are colored by the reality of the people around him. Morals are an interface between ourselves and the rest of the world.
Its a bad structure, but piro could wallow in self pity and simply become a puddle of useless ooze and be even worse without it. he compensates by beating himself up and completely negating any personal worth from what is making him feel down, which he uses to move on with the tasks of living. A miserable way to be? perhaps. its not easy being a self abusive passive agressive. But it doesn't mean his morals are out of line. He's got some traits that i think could lead him to a better approach to things. We'll see :)
(no idea where i got this concept of a piro's personality from... :)